The present invention relates to a liquid crystal display and, more particularly, to a low-consumption-power color liquid crystal display which is obtained by decreasing the size, weight, consumption power, and cost of a projection-type color liquid crystal display and suitably applicable to, e.g., a color liquid crystal viewfinder or a head mounted display used in a video camera or a digital still camera.
Recently, the image quality and resolution of liquid crystal displays are increasingly improving, and such liquid crystal displays are replacing cathode-ray tubes as medium- and small-sized displays such as personal computer displays.
As large-sized displays using a color liquid crystal display, projection-type liquid crystal displays (liquid crystal projectors) are marketed. This projection display has the advantage that a TFT liquid crystal display which is difficult to increase in size can be made small. In currently prevalent liquid crystal projectors, white light from a light source is divided into three primary colors of light, images of these three primary colors are formed by three pixels corresponding to these colors, and a color image is formed by using an optical system which focuses these images on one screen. Conventional three-panel projectors of this type are heavy and expensive because the optical system occupies a large space. To solve this problem, single-panel projectors are also being studied in which color filter patterns which transmit only three primary colors of light respectively, and absorb their complementary colors are formed in one liquid crystal cell.
Unfortunately, such single-panel projectors require a light source at least three times as bright as a light source of the conventional three-panel projectors, and this increases the consumption power. Also, light absorbed by the color filters causes color deterioration of the color filters and lowers the reliability. For these reasons, single-panel projectors have not been marketed yet.
Examples of small-sized displays using a color liquid crystal display are viewfinders used in video cameras or digital still cameras, and head mounted displays. Video cameras and digital still cameras except those for professional uses are supposed to be carried. Therefore, it is being desired to reduce the consumption power to meet the demand of battery capacity. Also, head mounted displays are preferably cordless when the ease with which these displays are mounted is taken into consideration. Therefore, low consumption power is being desired.
Liquid crystal projectors, liquid crystal viewfinders, and head mounted displays have the following common problem. That is, high resolution particularly decreases the pixel pitch when color filters are incorporated into liquid crystal cells. This decreases the aperture ratio and results in low light utilization. Low light utilization leads to an increase in the consumption power of a light source.
In consideration of the above situation, it is being demanded to establish a technology capable of reducing the consumption power of a high-resolution, full-color liquid crystal display.
Meanwhile, with advancing mobile communication technologies, development of liquid crystal displays as portable terminals is being sought. To use a liquid crystal display as a portable terminal, its consumption power must be reduced in respect of battery capacity. Therefore, a general conventional approach is to use monochromatic or multi-color reflection-type liquid crystal displays as portable terminals. However, with the spread of the Internet and the like, even a portable terminal is required to include a function of displaying high-quality, full-color image information. For the reasons as above, the image quality of the conventional reflection liquid crystal displays cannot satisfy the users. Accordingly, transmission-type color liquid crystal displays requiring a backlight are currently used even at the expense of battery capacity.
In a transmission-type liquid crystal display using a TN (Twisted Nematic) liquid crystal which is currently used most frequently, a backlight as a light source accounts for approximately 60% of the consumption power of the display. This is because most light from the backlight is absorbed by a polarizing plate and color filters, so the backlight is required to have a light amount including the loss of light absorbed by the polarizing plate and the color filters in order to ensure enough brightness. In a transmission-type liquid crystal display requiring a polarizing plate on the light incident side, the utilization of light from a backlight is limited to 50% in principle due to absorption by the polarizing plate. Additionally, to display color images, the light must pass through R, G, and B color filters. This further decreases the light utilization to 1/3. That is, together with the loss at the polarizing plate, the light utilization is limited to 16.7% in principle.
Recently, it is being attempted to reduce the light loss by absorption at a polarizing plate by using a backlight incorporating a polarization converting optical system (e.g., Jpn. Pat. Appln. KOKAI Publication Nos. 7-36032 and 7-36025). However, the problem of the light loss by absorption at color filters still remains unsolved in these attempts.
From the foregoing, it is being demanded to realize a full-color liquid crystal display which keeps the image quality of the conventional transmission-type liquid crystal displays and at the same time consumes little power.
As described above, a high-image-quality, low-consumption-power color liquid crystal display is being desired and has not been accomplished yet.